1. Field of the Invention
The present invention relates to an electrostatic discharge (ESD) protection structure, and in particular to an electronic device or a printed circuit board with a simplified ESD protection structure.
2. Description of the Related Art
As technology improves, electronic components become more and more complicated reducing the tolerance for electromagnetic interference (EMI) and electrostatic discharge (ESD). It is therefore conventional electronic devices require additional ESD protection circuits to protect important chips or other electronic components therein.
In most electronic devices, operating controls connect to specific pins of a chip to enable specific functions, such as controls for a CD drive or function keys of a mobile phone. Gaps between controls and the housing of the device, considerable electrostatic charges carried by users, which can enter circuits through air or direct contract, interfering with or damaging electronic components therein.
FIG. 1 shows a conventional ESD circuit of an electronic device. In FIG. 1, a control 10 is connected to a specific pin of a chip through a conventional ESD protection circuit 20. The ESD protection circuit 20 comprises a resistor 26, two Zener diodes 22a, 22b and two capacitors 24a, 24b. The positive pole of Zener diode 22a and the negative pole of Zener diode 22b are connected to the resistor 26. The Zener diodes 22a, 22b are individually connected to ground with the capacitors 24a, 24b connected in series to filter out high frequency noise. Electrostatic charges can be transferred to ground through the Zener diode 22b when the control 10 receives sufficient positive electrostatic charge, or through the Zener diode 22a when the control 10 receives negative electrostatic charge. Thus, the output voltage Vo of the ESD protection circuit 20 in unaffected by electrostatic charge, and electronic components are protected from EMI or ESD.
The conventional ESD protection circuit requires two Zener diodes, two larger capacitors and a distinct resistor. When an electronic device has a plurality of separately disposed controls, however, multiple ESD protection circuits are required to provide sufficient protection, thus increasing the cost of the device.